Electro-chemically activated (ECA) water is produced from dilute dissociative salt solutions by passing an electrical current through the solution to produce catholyte and/or anolyte products. The catholyte, which is the solution exiting the cathodal chamber of the activation reactor cell, is an anti-oxidant which typically has a pH in the range of from about 8 to about 13 and an oxidation-reduction potential (ORP) in the range of from about −200 mV to about −1100 mV. The anolyte, which is the solution exiting the anodal chamber, is an oxidant which typically has a pH in the range of about 2 to about 8, an ORP in the range of from about +300 mV to about +1200 mV or more, and a Free Available Oxidant (FAO) concentration of ≦300 ppm by weight.
During the electrochemical activation of aqueous saline solutions, various oxidative and reductive species can be present, for example: HOCl (hypochlorous acid); ClO2 (chlorine dioxide); OCl− (hypochlorite); Cl2 (chlorine); O2 (oxygen); H2O2 (hydrogen peroxide); OH− (hydroxyl); and H2 (hydrogen). The presence or absence of any particular reactive species in the solution is predominantly influenced by the derivative salt used and the final solution pH. So, for example, at a pH of 3 or below, HOCl tends to convert to Cl2, which increases the toxicity level of the product. At a pH of below 5, low chloride concentrations tend to produce HOCl, but high chloride concentrations typically produce Cl2 gas. At a pH above 7.5, hypochlorite ions (OCl−) are typically the dominant species. At a pH of greater than 9, the oxidants (chlorites and hypochlorites) tend to convert to non-oxidants (chloride, chlorates and perchlorates) and active chlorine (i.e. defined as Cl2, HOCl and ClO−) is typically lost due to conversion to chlorate (ClO3−). At a pH of 4.5-7.5, the predominant species are typically HOCl (hypochlorous acid), O3 (ozone), O22− (peroxide ions) and O2− (superoxide ions).
For this reason, anolyte will typically predominantly comprise species such as ClO; ClO−; HOCl; OH−; HO2; H2O2; O3; S2O82− and Cl2O62−, while catholyte will typically predominantly comprise species such as NaOH; KOH; Ca(OH)2; Mg(OH)2; HO−; H3O2−; HO2−; H2O2−; O2−; OH− and O22− The order of oxidizing power of these species is: HOCl (strongest)>Cl2>OCl− (least powerful). Therefore, anolyte can have a much higher antimicrobial and disinfectant efficacy in comparison to that of catholyte, or of commercially available stabilized chlorine formulations used at the recommended dosages.
The anolyte and catholyte solutions will typically be produced by electro-chemically activating a dilute aqueous saline solution comprising in the range of from about 1 to about 9 grams of salt per liter of water. The salt can be any inorganic salt. The salt will preferably be non-iodated sodium chloride (NaCl) or potassium chloride (KCl).
Prior to use, the electro-chemically activated anolyte product will typically be diluted with water. The diluted anolyte solution will typically comprise at least 50 parts by volume of non-activated water per 50 parts by volume of concentrated anolyte. More typically, the diluted anolyte solution will have a water-to-anolyte volume ratio of at least 60:40. In each case, the parts by volume ratio of water to concentrated anolyte will typically not be greater than 98:2, will more typically not be greater than 95:5, will more typically be in the range of from about 94:6 to about 60:40, and will most typically be in the range of from about 93:7 to about 65:35.
One type of reactor cell 1 used in the art for producing electro-chemically activated water solutions is depicted in FIG. 1. The reactor cell 1 is a flat plate reactor cell which comprises: a negatively charged cathodal plate 7 positioned within a container 2 on one side thereof; a positively charged anodal plate 6 positioned in the container 2 opposite the cathodal plate 7; a ceramic membrane 5 which is positioned within the container 2 between the cathode 7 and the anode 6; an anodal flow chamber 3 formed in the container 2 between the ceramic membrane 5 and the anodal plate 6; and a cathodal flow chamber 4 formed in the container 2 between the ceramic membrane 5 and the cathode 7.
Another type of reactor cell 11 used in the art for producing electro-chemically activated water solutions is depicted in FIG. 2. The reactor cell 11 is a cylindrical cell which comprises: a negatively charged outer cathodal cylinder 17; a positively charged, coaxial anodal rod 16 which extends through the cathodal cylinder 17; a coaxial cylindrical ceramic membrane 15 which is positioned within the cathodal cylinder 17 between the interior wall of the cathodal cylinder 17 and the exterior surface of the anodal rod 16; a cylindrical cathodal flow chamber (annulus) 14 formed between the ceramic membrane 15 and the cathodal cylinder 17; and a cylindrical anodal flow chamber (annulus) 13 formed between the ceramic membrane 15 and the anodal rod 16.
The anodal rod 16 will typically be formed of titanium and will be coated with an oxide of a platinum group metal such as iridium or ruthenium. The cathodal cylinder 17 will typically be formed of titanium.
The operation of the plate-type reactor cell 1 depicted in FIG. 1 or the cylindrical reactor cell 11 depicted in FIG. 2 can be varied significantly depending upon the particular solution properties desired. In one aspect, the properties of the electro-chemically activated product solution(s) can be varied by changing the flow rate of the aqueous saline solution through the reactor cell and/or by changing the amount of electrical current applied to the dilute saline solution. In addition, the product solutions and solution properties can also be altered by changing the flow pattern of the dilute aqueous saline solution through the reactor cell such that (1) the saline solution is delivered through the anodal chamber and the cathodal chamber in co-current flow; (2) the saline solution is delivered through the anodal chamber and the cathodal chamber in countercurrent flow; (3) a portion of the catholyte recovered from the cathodal chamber is recirculated through the anodal chamber; and/or (4) all of the catholyte recovered from the cathodal chamber is recirculated through the anodal chamber.
By way of example, in one application, it is known in the art that electro-chemically activated anolyte solutions can be added to foods, water, beverages, or pharmaceuticals, or can be used as disinfectants, purification agents, odor neutralization agents, flavor neutralizing agents, or for other purposes in food, water, beverage, and pharmaceutical processing systems. Prior to being diluted with water, the concentrated anolyte solutions used in these applications will typically be neutral or only slightly acidic solutions having a pH in the range of from about 5 to about 7.5, an oxidation-reduction potential (ORP) of at least +400 mV, a free available oxidant (FAO) content of ≦300 ppm by weight and a free available chlorine content (FAC) of 30-200 ppm by weight. These anolyte solutions will more preferably have a pH in the range of from about 6 to about 7.3 and will most preferably have a pH in the range of from about 6.5 to about 7.2. In addition, these anolyte solutions, in undiluted form, will most preferably have an ORP of at least +600 mV.
An example of a procedure used in the art for producing a slightly acidic or pH neutral anolyte product of this type using either a plate-type reactor cell 1 as depicted in FIG. 1 or a cylindrical reactor cell 11 as depicted in FIG. 2 involves the steps of: separately harvesting a concentrated catholyte solution from the cathodal flow chamber; reintroducing at least some of the catholyte solution into the anodal flow chamber, preferably in the absence of any fresh water; and manipulating the flow rate, the hydraulic flow configuration, and the pressure and temperature of the catholyte through the anodal chamber as needed so as to produce an anolyte solution that is characterized in that it predominantly includes the species HOCl (hypochlorous acid), O3 (ozone), O22− (peroxide ions) and O22− (superoxide ions), and has a Free Available Oxidant (FAO) concentration of ≦300 ppm by weight.
Unfortunately, however, one shortcoming of this procedure for producing a highly effective yet neutral to slightly acidic anolyte which is safe for human consumption is that a significant amount, or sometimes substantially all, of the catholyte is consumed by recirculation through the anodal flow chamber. Thus, oftentimes, very little or substantially none of the catholyte product can be independently harvested for other uses.
Another shortcoming of this procedure is that a significant amount of the chloride ions in the dilute brine feedstock are not converted during the electro-chemical activation process. The presence of a higher concentration of unreacted chloride ions in the anolyte product is viewed as presenting an increased risk of corrosion which could shorten the life of the reactor components and coatings.
Moreover, chlorides are already present in most water sources and the addition of any further chloride load can create concerns, for example, for beverage producers and other users of stainless steel processing equipment. In many cases, the original equipment manufacturer will not guarantee equipment which is exposed to chloride levels of greater than 55 ppm, and in some cases even less.
Unfortunately, to reduce the residual chloride content and increase the FAC levels of these anolyte products using a traditional prior art reactor system configuration, it would be necessary to use a high brine concentration, a very low flow rate, and an increased amount of electrical current. This would result in premature failure of the reactor system due to coating failure, and would also significantly reduce the amount of anolyte product produced.